Unsafe Cartridge Combination You Never Thought About

Have you ever thought that 7.62x39mm and .243 Winchester can be a pair of cartridges that are dangerous if mixed? Of course, any cartridge is dangerous if not used in a gun it is chambered for and nobody should do it. However, there are some pairs of cartridges known for causing catastrophic failures if mixed.

When we talk about dangerous combinations, what immediately comes to mind is .300 Blackout shot in a .223 Rem chamber. That is perhaps the most significant flaw of the .300 Blackout design. But cartridges like 7.62x39mm and .243 Winchester look so different –  they have different dimensions of cartridge head, case length and it is strange how could someone mix these two and how could they even chamber and be shot in each other’s chambers?

It turns out, that ball FMJ bullet of 7.62x39mm cartridge will get stuck in the .243 Winchester chamber just at a right spot where its primer would be positioned in the bolt face so that the action will close and the striker will be able to hit the primer. It kind of headspaces on the bullet. I assume that spot is where the neck portion in .243 Win chamber starts.

Again, nobody should mix cartridges, but accidents happen. Particularly to the gentleman in the video below. He chambered (not intentionally) a 7,62x39mm cartridge in a .243 Win rifle and shot it. The result was a blown up rifle because he was trying to push a .311 caliber bullet through a .243 bore.

Hrachya H

Being a lifelong firearms enthusiast, Hrachya always enjoys studying design, technology and history of guns and ammunition. His knowledge of Russian allows him to translate and make Russian/Soviet/Combloc small arms related information available for the English speaking audience.
Should you need to contact him, feel free to shoot him a message at TFBHrachyaH@gmail.com


  • lucusloc

    7.62x54r fits nearly perfectly in a .45 chamber. Not sure how dangerous it is, since the 7.62 would probably just blow out the muzzle, but it does go to illustrate that sometimes really odd fits are possible.

    • Gun Fu Guru

      You should test it and tell us the results.

      • lucusloc

        I have been shopping the idea around a few of the more trollish/silly guntubers. Maybe if we get more people involved one of them will grab a HighPoint and some string and try it out.

        • Gun Fu Guru

          I know that break-action shotguns gan have adapters that accept pistol cartridges. The rounds don’t build up enough power to require a long semi-ish barrel that rifle rounds need because the energy can go out the front. I wager to say that the chamber on a .45 isn’t strong enough to contain the blast and that the pistol will explode.

          • lucusloc

            Most of the case for the 54r is unsupported though, so it will split and relatively low pressure gasses will most likely blow out the muzzle. My guess is that it is mostly safe, but I’m not going to risk one of my guns trying it.

          • Archie Montgomery

            You are correct, lucusloc. I cannot see where such an event would do any benefit to the firearm; quite possibly leave trash in the barrel.

    • TechnoTriticale

      When the incorrect caliber is smaller than the incorrect firearm, the usual result is a split case and a wildly inaccurate round tumbling out at a lower-than normal velocity, accompanied by excess gas and perhaps more flash and noise.

      But that’s if the incorrect firearm is modern and strong. Modern smaller calibers in older larger cal. guns can be a hazard even without a tight bore seal. For example, .38 SPL, +P and .357 MAG (.357 diam) is a kaboom hazard in .38LC (.361 bore diam). A Colt 1892 DA (.38LC) will chamber the full spectrum of .357 38s, including .357 magnums. Only light wadcutters might not be expected to destroy the revolver, but are sufficiently inaccurate that there’s no point in risking it.

      • lucusloc

        Yeah, I suspect it would be pretty safe. Still don’t want to be the one to try it though.

        • mikee

          if you change your mind, make sure your will is up to date!

      • Chris

        Friend of mine loaded .270 win in his 30-06 accidentally ! ( he had a 270 and a 30-06 on this trip …270 was unloaded And packed away in the sled …the ammo from it were loose in his pocket ! )
        Then he saw a moose ,took aim ,fired and the bullet smacked the Moose’s lower leg ! He knew what the problem was,so he grabbed a 30-06 round from his pocket ,and loaded it, shot and and dropped the moose !
        The lesson he learned was never carry mixed calibers that can be chambered in same rifle ( .270 in 30-06 or .243 in .308 l ) when you shoot a smaller caliber in a larger barrel it usually just spoils accuracy and lacks power (although the Moose’s lower leg bone was shattered by the . 270 Shot from 30 -06 ! )
        BUT clambering a oversized bullet in a too small diameter barrel can be deadly !

        • Richard Lutz

          Crazy to have both a .30-06 and .270. The only general purpose centerfire round you need is the .308W. The .223/5.56mm is great for light medium game/varmint shooting/tactical use.

    • Art out West

      The only .45s I’ve ever had are a Glock 21 and a Colt 1917 revolver. I don’t think the 54R would fit in the Glock magazine, or that the cylinder would close on the revolver with a 54R round in it.
      No worries there for me.

      • lucusloc

        Apparently you are not trying hard enough.

      • .45

        .45 ACP carbine, with the bulk of the round extending into the barrel? I’m not taking one of my 1911s apart to check, but that sounds somewhat plausible. Of course, anything except a break action would be impossible to do that with…

        • .45

          Martini Henrys had .45 cal bullets…

          Maybe I should Google this…

          • Giolli Joker

            45-70, you’re welcome.

          • .45

            I believe the kids these days say “Derp” when they miss the obvious… Thanks though. I couldn’t see the forest, too many trees in the way.

    • Tassiebush

      My understanding of that situation is that the projectile fired from a much larger bore tends to go around 500-600fps and the gun is probably not subjected to heaps of pressure because it’s all loose. I recall pipe guns using old ww2 .50bmg leftovers in the Solomon Islands civil war. Not sure I’d want to try it though.

  • Raptor Fred

    Huh that’s interesting.. Makes you think how many other crazy incorrect combos are out there?

    • Anonymoose

      I don’t want to know. Just keep your stuff straight!

    • PK

      Lots. Lots and lots and lots. It’s why boxes of ammunition usually have a statement about firing only in the correct caliber of firearm.

    • lucusloc

      Grab a whole bunch of dummy rounds in as many cartridges as you can find and head out to your local big box retailer. Then ask to fondle all the guns, especially the ones chambered for less common cartridges.

      • Raptor Fred

        Hahahaha, there is no way you would end up in handcuffs and on the national news. Love it!

        • lucusloc

          You provide the dummy rounds, I’ll find a sucker subject to run the tests. . .

    • Tassiebush

      8mm Mauser has wrecked plenty of 3006 I believe. A problem in the days of abundant surplus.

      • Jim_Macklin

        Some 8mm Mauser use 0.323 bullets and some use 0.318. Certainly good for a blown primer and a test of your shooting glasses.

  • Some Rabbit

    Good point, I’ve been guilty myself. Too many different guns and loose ammo on the shooting bench. Probably a good practice to get into is when you’re done shooting one gun, remove it and all it’s ammo from the bench before getting out the next gun.

    • Renato H M de Oliveira

      And double /triple /quadruple check before loading!

  • Kivaari

    I had a friend insert a .270 in a 7mm Rem Mag. He shot at a deer about 50 yards away. The deer was hit, ran a few yards and dropped dead. There was brown smoke coming from the action so he opened the action only to see the cracked and fire-formed casing. What the heck he had a dead deer. He recovered the slug, it had hit sideways (keyholed) but it was bent into a u-shape. One of those rare events when the wrong shell resulted in injurines only to the deer.

    • Dougscamo

      Surprised that he didn’t get hit in the face by powder from the split case! That’s a lotta gas roaming around in that chamber; don’t ask me how I know.

      • Archie Montgomery

        Doug, most modern rifles are built with ‘channels’ to direct gases away from the shooter in event of a case failure. Case failure happens with the proper ammunition as well. However, as the .270 Win cartridge uses a .277″ bullet and the 7mm Magnum has a .284″ bore, most of the gas – and pressure – simply vents down the barrel. Very little tendency for the burning gases and pressure to ‘back up’ through the action.

        In fact, that’s a fairly benign mis-match. Not a good idea as the results might be more damage to the rifle than the shooter. And I’m amazed the bullet actually hit the deer. However, it isn’t likely to cause the action to fail and disintegrate.

        • Dougscamo

          I said don’t ask me how I know why….and the why is I have been hit with powder and gases before from split cases and this has made me a steadfast user of safety glasses.
          Not saying that the rifle would be destroyed…

          • Archie Montgomery

            I had a primer puncture on my 6.5×55 Swede once. The escaping gas was properly diverted and it just sort of elevated like smoke from the bottom of the action. Didn’t affect me physically, but when I realized what had happened, my major intestine was – ah – ‘invigorated’.

            I agree, safety glasses are part of the shooting kit. Not to mention, I’ve fired more than one ‘old’ rifle – with correct ammunition – by tying it to a tire and activating the trigger with a string or cord. (No one else on the range, either.) By no means do I suggest doing anything self-destructive.

    • Richard Lutz

      Crazy to have both a .270 and a 7mm Rem Mag. The only general purpose centerfire round you need is the .308W (anything substantially more powerful causes most people to develop a flinch). The .223/5.56mm is great for light medium game/varmint shooting/tactical use.

  • Disarmed in CA

    If you can’t read the headstamp, don’t forget your readers, or keep everything in a box un-mixed..

  • How did someone even manage to get a .243 into their x39? I mean, seriously. it won’t fit in a mag, it won’t drop into the gun easily…I’m calling BS.

    • Hrachya H

      It was exactly the opposite.

  • 22winmag

    Skip the video.

    No gratuitous kaboom!

  • El Duderino

    Doesn’t .458 Win Mag mis-fit in some obscure chamber?

    .45/70 in a .410 shotgun is always good for some laffs.

    • mikee

      Are you auditioning for the Darwin awards?

    • G

      458 Win Mag has a normal belt but 450 Marlin doesn’t. You are not supposed to be able to chamber a 450 Marlin cartridge in a “normal” magnum rifle for that reason.

    • Archie Montgomery

      Dude, from the sizes of the heads and belts, most any belted magnum case would fit into the chamber and be held up again the bolt face of a .458 Win Mag rifle. However, as the other rounds have smaller diameter bullets, I doubt is enough pressure would develop to do much, including sending the bullet down range.

      A rather dopey waste of expensive ammunition and potential damage to the chamber when the case splits. (Scarring and pitting, mostly.)

      • El Duderino

        I was talking about the other side of it — I don’t remember the chambering, but .458WM fits in some smaller bore and will definitely cause a bad day (or a good one for your life insurance beneficiary). I can’t seem to find what I’m thinking of using Google-fu.

        • Archie Montgomery

          I haven’t researched it – not having any belted magnums and not being impressed with the concept – but the possibility would exist IF the .458 WM loaded cartridge was shorter than the chamber of the rifle. That is, the loaded .458 WM cartridge would have to be shorter than the shoulder of the other cartridge.

          Doing a quick perusal of Cartridges of the World, I think there is a possibility this might be possible if inserting a .458 WM in a .416 Remington or one of the large Weatherby magnums.

          I am somewhat in awe (not in a good way) of someone who might confuse a loaded .458 WM with anything by Weatherby. The .416 Remington is ‘similar’, but the Remington cartridge CASE is enough larger in diameter the .458 WM would be rather loose in the chamber.

          Not to mention I’m in awe of the spending money of one who not only owns a couple of these rifles, but takes them both shooting.

  • Bucho4Prez

    .243 is relevant again!

  • gunsandrockets


  • Klaus Von Schmitto

    In other news, it’s been found that beating on a 155mm M795 with a ball pein hammer is dangerous.

    • Marcus D.

      My father “volunteered” (meaning he found his name on the volunteer list one day) to test US Army equipment in Alaska during the winter in 1947-48, should the need arise to fight the Russians in Siberia. The average temperature north of the Arctic Circle in winter that year was minus 46 degrees. Among the numerous acci8dents and failed equipment, one of them was that the breach of their howitzers would slightly shrink form the cold, and the shells would jam when being loaded. One wiz kid tried to beat one in with the brass end of another (live) shell. It did not turn out well for him or the other members of his gun crew. Barrels would also shrink, and he had more than one photo of field howitzers missing half the barrel.

  • Paul B.

    Same thing with .308 Winchester chambered in a .270 rifle.

    • Jim_Macklin

      No it isn’t. The .0.308 bullet has to fit into a 0.274 bore. The case will split but it will seal enough to raise pressures high enough to blow the case head. Particularly since many .270 Winchester’s are cone breech Model 70 with an unsupported head.
      A .458 Winchester would probably chamber in a .375 H&H or .338 W https://uploads.disquscdn.com/images/eac2cf3abc765677ba44cedb32b40221bae0a3fbce9ae9f6b8343da3847f7f82.jpg eatherby, but if anybody has a rifle they don’t care about blowing up, I suggest you strap it to a heavy truck tire and use a 100 foot rope from a trench to fire it.

  • Herp

    My dad is a hunter, but in no way is he a “gun guy”. I was at his house a while back and his rifle and ammo were still out from deer season. I looked down at the open foam inner box that was lying out and saw he had a few of his friend’s 7.62×39 mixed into his .300 savage box. They did look pretty similar. I let him know, but I’m sure he forgot and will blow his gun up next year.

  • Jim_Macklin

    I found a 7.62×39 unfired but the case was marked. Best I could figure was somebody tried to chamber it in their Winchester 30/30.

    Most Walmart clerks don’t know one 30 caliber from another.

  • Brasstard

    I found 2 30-30 cases that had been fired in a 303 British chamber one time out in the desert. One case had split and both had fireformed to look like 303 brass.

  • Capn Jack

    As kids, we always used to wonder if a .32 Spl. would shoot in a .410 shotgun. It would chamber, but no one ever had the guts, or was foolish enough to pull the trigger.

  • Qoquaq En Transic

    I remember seeing some guys shooting 7.62 NATO in a 30.06 barrel in a 1919 BMG.

    Ran fine but those copper-washed steel cases (Norinco) 7.62 came out looking like some monstrous straight-walled round… with a mean crimp!

    • iksnilol

      Happens in Norway with 30.06 Mausers. The resulting fire formed brass is usually called 30. Idiot.

      • Qoquaq En Transic

        I was pretty shocked to see 1919 BMG owners running belt after belt of Norinco steel-cased 7.62 NATO through their 30.06 barrels with no problems.

    • Archie Montgomery

      If one is careful, one can ‘fireform’ an empty .308 Winchester case in a .30-06 chamber. Then carefully trim the open end and one has a wildcat cartridge called “.45 Very Long Auto”. I am not aware of any arms for it yet.

  • Tom Currie

    There are numerous combinations that CAN be chambered. But there are only a few such combinations that are likely to occur accidentally without a level of carelessness or stupidity worthy of Darwin Award consideration.

    .300BO in 5.56mm is the one we hear about the most — for fairly obvious reasons.

    20ga dropped into a break action 12ga shotgun followed by a 12ga round properly chambered on the obstructed barrel is another combination we used to hear about occasionally before .300BO grabbed all the attention.

    As another poster mentioned, several flavors of 7.62x?? will chamber in various .45 chambers (although doing that “accidentally” is stretching credibility).

  • Palmier

    Here is a good one that happened to me, .40 SW in a .45 carbine. The .40 loaded and slide halfway down the barrel. Pull back the bolt, see an empty chamber, assume failure to feed and then load and fire a .45 into the back of the .40…its like a squip load….that also explodes.

  • roguetechie

    Probably the single best piece of advice I ever got was that ammo boxes are too cheap to reuse a box designated for one caliber for a different caliber!

    I literally have a can of krylon and a couple giant sharpies in my shooting gear that have exactly one purpose in life, marking ammo cans on all 6 sides with their designated caliber!

    It has saved me countless aggravation and blown up guns when taking gun newbies out shooting for the first time.

    It’s the first layer in my own personal safety onion I habitually practice…

    It’s sort of like good hygiene, it only counts if you do it every time!

    • Gun Fu Guru

      It’s common sense like this that makes me feel no sympathy for the “I thought .300BLK was .223Rem” excuse.

      • roguetechie

        Safety and not blowing up guns I can’t just defecate out money to replace on command is how I afford firearms as a hobby at all…

        That and home building anything and everything possible with the implicit understanding that dollars spent on tools, repair manuals, and sometimes just buying someone who knows something I need to know a beer in order to get their knowledge is money which is NEVER a waste!

        The only downside is that building guns launched me into the secondary supporting hobby of building tools and tooling with which I can build more guns!

        • Archie Montgomery

          I cannot afford to replace or rebuild guns at whim, either.

          Not to mention, eyeballs are even more expensive. And my face is not the prettiest face on Earth, but I’ve had it ever since I was a little kid and have grown rather attached to it.

          • roguetechie

            I know what you mean… I finally got glasses recently and my insurance only paid for a small portion of it, so I wear revision prescription shooting glasses around every day like a goon because a pair of shooters and a pair of shooters wasn’t an option LOL!!

            But, at least I’m protected from shotgun pellets to the eye socket while riding the commuter train every day haha

          • Archie Montgomery

            You’re also protected from the windows being broken and getting in your eyes. Try not to act like a conspiracy devotee.

            Unless you want to avoid conversations on the train.

          • roguetechie

            You’re missing the point of this post entirely….

            Walking around in what are pretty obvious to most people as some sort of “tactical eyewear” makes you seem at the very least antisocial!

          • Archie Montgomery

            Ah. I think that last comment depends on where one lives. I have a set of ‘shooting’ glasses (spectacles), with my close range prescription (so I can see the sights), shatter-proof lens and side covers to prevent bits from getting in my eyes.

            This sort of spectacles was developed for persons in various industrial occupations, like machinist, saw operators and so on. I used to live in Los Angeles County (PDSR California) and people wore much stranger things in public.

            Depending on how you dress otherwise and deport yourself, I wouldn’t think most normal folks would consider you ‘anti-social’.

            However, matters of dress – including ‘accessories’ like spectacles and head coverings and lapel pins – are matters of subjective taste and local cultural ‘rules’. Still, your choice seems to be either wear the ‘strange’ glasses and look like a goon (your words), or not wear them and have limited vision. You’re a big kid.

          • roguetechie

            Yeah, it’s definitely a regional issue for me. When I lived in Salt Lake no one thought anything of someone wearing safety glasses or a set of sawflies to Applebee’s…

            And in Wyoming I ran into a guy on a job site once who when we counted the guns in his truck broke 37 after digging around a toolbox in the back!

            Same guy also taught me to shoot his Barrett off a gun nest we built on the roof of the rich guy cabin we were building. You could always tell it was lunch time by the booms coming from the job site!

            So yeah, it’s always going to depend on who exactly you have to interface with on a daily basis.

  • Jimmy D

    This is why I only set off randomly discovered cartridges by clamping the projectile facing downward in a vise and smashing the primer with a hammer. Safety first!

    • Nashvone

      When I was a kid, a buddy found an old box of 12 gauge shells for a shotgun his dad had gotten rid of. He took them out in the woods and strapped them to a tree with plumber’s tape and proceeded to shoot the primers with his .22. His dad took his rifle away for a long time for that stunt.

  • Dan Desnoyers

    Perhaps I am confused, but owning a firearm and knowing what ammunition it uses should go hand in hand. If the picture at the beginning of the article actually shows the two different cartridges, how would a person confuse 7.62×39 for .243 Winchester when loading the magazine? The 7.62×39 is clearly a much shorter cartridge with a much larger projectile. Once again, perhaps I am confused.

  • SPQR9

    SAAMI used to have a Web page listing unsafe combinations.

  • 3 of 11

    I have witnessed someone fir, 6.5 Japanese in a 7.7 Japanese chambered Arisaka. Guess those suckers are strong and this guy was dumb enough to not notice since he put two through and was preparing a third before being stopped by the RSO upon inspecting his brass which was visually obsiously FUBAR from ground to standing eye level.

  • robert matthews

    personally I would always use the same ammo,and brand of ammo as recommended by the manufacturer…Had some extraction problems on a Sportco 71S 22LR…was using ammo not manufacturer recommended..insufficient power to operate action/extract properly

  • Verner

    Some .300 WinMag rifles will chamber and fire the .30-06. Just don’t expect any kind of accuracy afterwards. In the case I saw, it messed up the rifling pretty well.

  • commenter1

    .308 Win can be made to chamber and fire in some 7.62x54r rifles. Not a recommended practice, however.

  • pismopal

    There is a difference between “fit” and “accommodate”. Just because a round can be accommodated doesn’t mean it fits.

  • JamesDrouin

    Darwin’s theory on evolution on display.

  • bthomas

    This sort of thing happens when people don’t pay attention. Plenty of instances where people shooting M-1 Garand rifles at a match got hold of 7.62mm rather than .30-06. It can be chambered. It will fire. The round will impact low on the target. The empty casing will look “weird.”

  • John Walker

    How exactly would one chamber a 300 blackout in a 223 rifle? It seems to me the bigger bullet is a fail safe, like you can’t put a 308 in a 243 or a 30-06 in a 270, etc…

  • Richard Lutz

    How many different rounds do you need?

    .177 pellet (best airgun caliber for target shooting/small pests).
    .22 LR (by far the best small game round).
    5.56mm (the best assault rifle round in the West – best in a FN Military Collector M4)
    .308W (kills elephants with 220-gr RN solids/great deer round with 125-gr HP).
    9mm (by far the best semi-auto combat round – best in a Glock 19).
    .357 Magnum (will penetrate bear skulls with heavy hard cast flat nosed solids).

  • Anthony “stalker6recon”

    I love my firearms, but I never took more than two at a time to the range, one long and one short. This way, I never am able to mix ammo even under the most distracting situations. I never did this to avoid mixing ammo, just to focus on proficiency on two weapons rather than just throwing lead with as many toys as possible.

    Without intent, I have avoided this dangerous situation from ever occurring.